I tried GNU octave with some of our devices today including the 6000 series but unfortunately did not work. I found that their implementation of the Instrument Control Toolbox is incomplete in comparison to Matlab and therefore missing some of the many functions required. It seems the functions they have included so far are only the NI VISA specific functions.

Our Matlab examples require many functions from "The Generic Instrument Drivers" and "Instrument Driver Editing and Testing" sections of the Instrument Control Toolbox. Some examples include: 'icdevice', 'connect', 'get', 'set'.